H.W.G. Meesters

Abstract

Coral reefs are vital ecosystems that face significant challenges such as eutrophication, an increase in nutrient levels in aquatic systems, contributing to the decline of coral reefs. This poses a global threat (Ban, Graham, & Connolly, 2014; Adam et al., 2021), often resulting in shifts from coral-dominated to algae-dominated ecosystems (López-Londoño et al., 2021). As part of the project "Restoration of Resilience of Nature and Society in the Caribbean Netherlands," extensive research and data collection are carried out on various Caribbean islands, including Bonaire, St. Eustatius, and Saba. To gain deeper insights into land-sea interactions, water quality monitoring, including nutrient data collection, is conducted across these islands.This study investigates the variations in nutrient concentrations across the West Coast of Bonaire and Klein Bonaire. With the focus on key nutrients PO43-, NH4+, NO2−, NO3−, and the sum parameter DIN, in the marine environment, insight into the water quality state is gained. The data utilized for this research spans from November 2021 to January 2023, with the focus on the year 2022. The nutrient measurements were systematically conducted at 11 locations across the gradient of the West Coast of Bonaire and around Klein Bonaire, covering both 5-meter and 10-meter depths.

For this research, the significant influence of the temporal and spatial factors; Month, Location, and Depth were examined for each nutrient, in combination with the established thresholds.The results revealed a consistent, increasing, or decreasing trend for the different nutrients over time, all significantly influenced by both temporal and spatial factors.Although high concentrations were found for all locations and nutrients, only two locations in the North of Bonaire were found to pose a risk to the health of the coral reefs and water quality.

This study provides crucial insights into nutrient dynamics, temporal variations, and spatial changes in Bonaire's marine environment. The identified patterns and risk assessments offer valuable guidance for targeted conservation efforts aiding in the preservation of Bonaire's coral reef ecosystems amid ongoing environmental challenges.

More information; https://research.wur.nl/en/publications/temporal-and-spatial-nutrient-va...

Abstract

Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2 , has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1- 5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish genetic diversity or as a storehouse of diversity that can be utilized if needed for restoration practices.